Due to the damage of the vertebra or bone, various methods of embedding artificial material into the body have been used. Particularly, due to the damage of various kinds of joints, vertebrae and bones, the total joint arthroplasty and re-operation on knee joints or hip joints have been widely used. In this case, in order to replenish the bone loss associated with such arthroplasty and the operation, a bone cement is used to fix the artificial material embedded in the body.
Bone cements, each of which is a material for reinforcing fluidity, primarily serve to replenish the bone loss attributable to a bone fracture or a surgical operation or serve to transfer mechanical loading between an implant and bone by stabilizing the implant. Bone cements are broadly classified into polymer bone cements and ceramic bone cements. Here, a ceramic bone cement includes calcium phosphate (including apatite) and bioceramics having biocompatibility as main components, and is frequently used as an alternative to bone loss because it has excellent biocompatibility to tissues in the body. However, since a ceramic bone cement has low strength, a bone cement is generally used to fix an artificial material such as an implant instead of ceramic bone cement.
A bone cement includes a powder component and a liquid component. At the time of operation, these powder and liquid components are mixed with each other to form a paste, and then the paste is used. The powder component includes polymethyl methacrylate (PMMA) as a main composition, and, in a commercially-available bone cement, the powder component may include a copolymer of methacrylate and styrene as a main component. Further, the powder component includes benzoyl peroxide, which is a free-radical polymerization initiator. Further, the powder component includes barium sulfate or zirconium oxide, which is a radiopacifier, in order to enhance opacity to X-rays. Furthermore, the powder component includes gentamicin or the like as an antibiotic for preventing the infection of bacteria during an operation.
The liquid component includes methyl methacrylate, which is a monomer as a main component. Further, the liquid component may include N,N-dimethyl-p-toluidine (or dimethylaminophenyl ethanol). N,N-dimethyl-p-toluidine acts as a free-radical activator to accelerate the formation of free radicals. Furthermore, the liquid component includes a very small amount of hydroquinone as a stabilizer to inhibit a self polymerization reaction when storing the bone cement.
When the powder component and the liquid component are mixed with each other, the mixture's viscosity is rapidly increased in proportion to the dissolution rate of polymer powder in a liquid monomer under an initial state of high fluidity, and thus the mixture thereof is formed into a doughy mixture. At this time, exothermic radical polymerization starts. That is, the exothermic radical polymerization is performed by reacting benzoyl peroxide, which is a polymerization initiator included in the powder component, with methyl methacylate, which is included in the liquid component. In this case, the polymerization degree, strength, porosity and residual monomers of the bone cement are determined by the freedom degree and concentration of free electrons, which are caused by the initial viscosity. Such a doughy mixture is solidified by polymerization and serves to fix an artificial implant.
In a surgical procedure involving a bone cement, when a powder and a liquid components are mixed with each other to form a doughy mixture having a predetermined viscosity (at this time (dough time), the doughy mixture does not adhere to surgical gloves (powder-free latex gloves)), the surgical procedure thereof is performed at the time of clinical application, that is, at the time that the bone cement that easily adheres to the bone loss portion is injected into the human body. Therefore, the surgical procedure includes the steps of mixing, waiting, dough, and working. Further, the surgical procedure may further include the step of setting in which working is no longer able to be conducted because of the deterioration in the viscosity attributable to polymerization in the doughy bone cement. Mixing, waiting, working and setting are greatly influenced by the characteristics (for example, the bead size, molecular weight, swelling characteristics thereof to non-crosslinked MMA monomer) of the PMMA polymer and by the working temperature.
Therefore, the doughy bone cement best adhere to the portion where there is bone loss when the polymerization characteristics of the doughy bone cement and the injection timing thereof are synthetically determined. That is, when the doughy bone cement is applied to bone tissue, the free radical polymerization in the doughy bone cement rapidly accelerates while the surrounding temperature rises from room temperature to body temperature, so that the elasticity of the viscoelastic doughy bone cement increases, with the result that the diffusion of radicals and monomer molecules decreases, thereby rapidly reaching the setting time. Since operation is physically limited when the elasticity of the doughy bone cement rapidly increases, the viscoelastic doughy bone cement is applied to the periphery of bone tissue or hardens when the polymerization characteristics of the applied doughy bone cement are not accurately understood and the injection time of the doughy bone cement is decided excessively rapid or slow. Therefore, various mixing and dispensing apparatuses for minimizing the differences in the application of a bone cement attributable to the different clinical experiences of doctors are being actually developed.
Meanwhile, general powder-liquid bone cements are classified into the two categories of low-viscosity bone cements and high-viscosity bone cements, depending on the initial viscosity thereof. A low-viscosity bone cement, which has high initial fluidity, is advantageous in that it can be sufficiently prepared before work starts because the time it takes bone cement to form a doughy bone cement is long, but is problematic in that its operation time becomes long. A high-viscosity bone cement, which has low initial fluidity, is problematic in that it must be rapidly applied because it hardens rapidly. However, the high-viscosity bone cement is advantageous in that it does not mix with blood because it can endure the pressure of bleeding occurring at the periphery of the bone tissue treated with a bone cement, and in that it can be rapidly applied to the bone tissue. However, in the application of high-viscosity bone cement, a vacuum mixer for preventing the introduction of air, due to the high viscosity of a bone cement, during the mixing process and a high-pressure injector for injecting a high-viscosity bone cement must be additionally used. These vacuum mixer and high-pressure injector are gradually becoming diversified and complicated. Such a diversified and complicated mixer and injector function to reduce the clinical difference attributable to the complicated polymerization characteristics of a bone cement, but are problematic in that the time it takes to apply a bone cement is lengthened due to complicated mixing and injecting processes, and instruments necessary for each of the processes must be purchased, thus increasing medical expenses.